The present invention relates to an improvement in shield structure of an electronic equipment, particularly of a synthesizer unit or a voltage control oscillator to be employed in a mobile telephone or the like.
Generally, in an electronic equipment to be employed in a mobile telephone, the countermeasure to vibration and noise is more strictly controlled than a stationary equipment. A general construction of such an electronic equipment is shown in FIGS. 4 and 5.
Referring to FIGS. 4 and 5, the conventional electronic equipment is generally composed of a box 1 having an opening, a printed circuit board 2 to be accommodated in the box 1 and having an integrated circuit (IC) 2a on one surface, electronic parts 2b such as chip resistors and capacitors on the other surface and connector terminals 2c, and a shielding cover 3 for protecting the electronic parts 2b and shieldably closing the opening of the box 1 for the purpose of shielding an oscillator incorporated in the IC. After the cover 3 is soldered to the box 1, the assembly is mounted on a printed circuit board 4 of a mobile telephone set. In mounting the assembly, earth tabs 1a projecting from the opening end of the box 1 are inserted into earthing through-holes 4a formed through the printed circuit board 4, and are fixed by soldering 5 as shown in Fig. 5. Reference numerals 1b formed in the box 1 designate stoppers for receiving the end portion of the printed circuit board 2.
FIGS. 6, 7 and 8 show a conventional shield structure. The box 1 is formed at its opening edge with substantially central four recesses 1c, and the cover 3 is formed at its peripheral edge with four projections 3a to be engaged with the recesses 1c. After the cover 3 is positioned in the opening of the box 1, the cover 3 and the inner peripheral surface of the box 1 are entirely fixed by soldering 6.
However, in the above-mentioned conventional shield structure, there must be provided a step for forming a space where the solder 6 is to be piled up between the opening edge of the box 1 and the upper surface of the cover 3. This step must be made as large as possible since a large amount of solder must be piled so as to prevent a solder crack due to a sudden change in temperature. Therefore, the equipment is hindered from being made compact because of the provision of this step. Furthermore, the solder 6 tends to flow through the recesses 1c of the box 1 to the outer surface of the box 1, causing a stain in appearance and bad soldering. Moreover, since the inner peripheral surface of the box 1 contacts only the peripheral edge of the cover 3, the solder 6 tends to flow into the box 1, causing short circuit of the electronic parts 2b.